This invention relates to a screw compressor ice making systems for use in ice making plants of direct expansion type artificial skating rinks using R22 (CHF.sub.2 Cl), R502 and R717 (NH.sub.3) as refrigerant.
In the past, artificial skating rinks have used indirect refrigeration systems to make ice. In these systems, a secondary refrigerant such as brine or glycerine is cooled to a temperature below the freezing point of water through direct expansion of a primary refrigerant in an evaporator. This secondary refrigerant is then pumped to the rink piping system to make ice. Because indirect refrigeration systems rely on the temperature difference between the secondary refrigerant and the skating rink to remove heat for ice making, they are inefficient and consume a lot of electricity. Also, the surface of the ice in rinks using these systems is easy to melt because the amount of heat conduction is limited by the temperature differential between the secondary refrigerant and the rink.
Modern artificial skating rinks usually use direct expansion refrigeration for ice making. In these systems, a refrigerant liquid, such as freon or ammonia, flows directly in the rink piping system. Heat is transferred from the ice to the refrigerant because of the temperature difference between the refrigerant and the ice layer, and because of the latent heat attendant to a phase change of the refrigerant from the liquid to the gaseous state. Direct systems use 45% to 60% less electrical energy compared with indirect refrigeration systems. Also, if there is sufficient refrigerant liquid inside the rink piping system, the refrigerant liquid can evaporate and absorb heat at any time thereby making the surface of the rink harder to melt.
Ice making systems for artificial skating rinks generally use open-type reciprocating compressors rather than semi-hermetic screw-type compressors. These systems are generally put together in a disorderly fashion, and, although some ice making systems come as packaged units, they are not put in single rows nor in symmetrical arrangements. Packaged units which do employ screw compressors often have them installed in the middle or the lower position rather than in the upper-most position. These units have high shipping costs because they are bulky and cannot be transported in a container. These units also increase the total building costs of a rink because they occupy a large floor area.